LIDAR systems are known to be utilized in a number of different arrangements including, but not limited to, “radar guns” as used by police to monitor traffic speeds, ground-based surveying, underwater scanning, airborne geo-mapping arrangements, aerosol monitoring, and the like. LIDAR systems may operate on the basis of various types of optical output signals, including continuous wave (CW) Doppler, pulsed Doppler, CW phase-shift keying (CW-PSK), pulsed PSK, and the like. In one exemplary arrangement, the LIDAR device emits a short pulse of infrared light that is directed in a narrow beam toward a selected target. The light pulse strikes the target and is typically reflected back towards the LIDAR device. This return energy is then captured by an optical receiving element and converted from light energy to an electrical signal. A high speed clock is used to determine the total trip time, which can then be used to calculate the range to the target. For speed calculations, multiple ranges are taken and the change in range over a short period of time is determined. Typically, police LIDAR speed guns and survey range finders use stripe array laser diode emitters to emit the pulse of infrared energy required to measure the distance to targets at significant ranges. The maximum range that a system can achieve is proportional to the amount of energy emitted per pulse by the laser. The amount of energy that is emitted from these lasers is typically limited by the laser safety regulations of the country where the LIDAR units are sold, impacting the maximum range over which these devices may be used.
LIDAR units are also starting to be used in automotive applications for driver assistance situations. Typically, these units have a range and field of view to detect objects, such as other automobiles, at an appropriate distance to take any necessary action, such as warning the driver or changing the speed of the automobile. In order to obtain the required field of view, prior art systems use two methods. One prior art LIDAR system consists of a phased array, which consists of several optical transmitting elements whose relative phase is adjusted to create a radiation pattern of constructive and destructive optical waves, forming a beam that can be electronically steered, by adjusting the phases of the individual optical transmitting elements. This phased array system is generally too expensive for use in the automotive environment.
In another arrangement, aerosol LIDAR systems may be used to detect aerosol clouds that may include biological weapon agents. In this case, multiple laser sources are used, operating at different wavelengths, to generate a large set of optical scattering data that is used to develop a “signature” of the aerosol and ascertain its chemical content. However, present technologies, owing to the complexity and laser power levels required for aerosol LIDAR, are limited in range and not well-suited for an in-the-field, portable detection system.
In these and other environments, therefore, a need remains for a LIDAR system that is relatively compact and portable, yet sufficiently precise for more complex applications.